Interactions between transcription termination protein rho of Escherichia coli and RNA polymerase and RNA are being studied by several approaches. Pure rho from mutants originally isolated as suppressing a polar insertion mutation in the lacZ gene is being characterized enzymologically. Preliminary results indicated that rho-115 ATPase is inactivated by the RNA homopolymer poly C at high temperatures. This experiment will be extended to other synthetic and natural RNAs, and to rho purified from additional rho mutants selected by the same or different genetic procedures. Rho from a rho-115 strain carrying a closely-linked second-site suppressor is being studied to determine if the second mutation affects any rho function in vitro. Rho-like activity from the gram-negative plant pathogen Erwinia carotovora will be compared to that of E. coli for transcription termination characteristics with homologous and heterologous RNA polymerase. A possible mechanism of rho mutant lethality, i.e., reduction in quantity of mRNA coding for some essential function, will be examined in rho-15 mutants that cause a nutritional defect in a particular genetic background. To look at interactions of the Beta subunit of RNA polymerase, second-site mutations that affect the phenotype of rpoC-32 cells of Salmonella typhimurium will be isolated and screened genetically and biochemically.